package cn.zhoumingxin.Test;

import java.util.Scanner;

public class TestDistance1 {
	public static void main(String[] args) {
		
		Scanner in = new Scanner(System.in);
		
		double x1;
		double x2;
		double y1;
		double y2;
		
		x1 = in.nextDouble();
		x2 = in.nextDouble();
		y1 = in.nextDouble();
		y2 = in.nextDouble();
		
		double A = Math.pow(x1-x2, 2);
		double B = Math.pow(y1-y2, 2);
		
		double distance = Math.sqrt(A+B);
		
		//进行计算，两点之间的欧式距离
		System.out.println(distance);
	}

}
